1. Field of the Invention
The present invention relates to a surface mounting type antenna which is a small-sized antenna applicable to two frequencies used in a mobile communication apparatus such as a cellular phone, an antenna apparatus, and a radio communication apparatus using the surface mounting type antenna and the antenna apparatus.
2. Description of the Related Art
Reduction in size for a mobile communication apparatus such as a cellular phone has been advanced rapidly. Concerning an antenna that is a component of the mobile communication apparatus, efforts have been made to cope with the reduction in size using a surface mounting type antenna and the like. An example of a conventional surface mounting type antenna and an antenna apparatus using the surface mounting type antenna will be explained with reference to a perspective view of FIG. 4.
In FIG. 4, reference numeral 61 denotes a surface mounting type antenna, which is mounted on a mounting substrate 72 to constitute an antenna apparatus. In the surface mounting type antenna 61 shown in FIG. 4, reference numeral 66 denotes a rectangular parallelepiped base body; reference numeral 65 denotes a feeder terminal; and reference numerals 62 and 63 denote radiation electrodes. In addition, in the mounting substrate 72, reference numeral 74 denotes a feeder electrode, and reference numeral 73 denotes a ground conductor layer.
In a structure of the conventional surface mounting type antenna 61, in order to make the surface mounting type antenna 61 applicable to two frequencies by changing pitches of the radiation electrodes, that is, to allow the surface mounting type antenna 61 to cope with different two frequencies, on a side of the base body 66, a pitch of the spiral radiation electrode 63 connected to the feeder terminal 65 is made coarse, and a pitch of the spiral radiation electrode 62 connected to the radiation electrode 63 is made dense.
Such a surface mounting type antenna 61 is mounted on a surface of the mounting substrate 72 by connecting the feeder terminal 65 to the feeder electrode 74, whereby an antenna apparatus 71 applicable to two frequencies is constituted.
In addition, as an antenna applicable to two frequencies, for example, Japanese Unexamined Patent Publication JP A 2002-204120 discloses an antenna for a mobile communication terminal that is adapted to be used in plural frequency bonds including frequency bands different from a predetermined frequency band by connecting a ground capacitor to an antenna element for the predetermined frequency band to change a value of the predetermined frequency band. According to this disclosure, since a switch is never inserted in series in a transmission path for transmission and reception signals, an antenna, which can cope with plural frequencies without causing a problem of a signal transmission loss, is obtained.
Further, for example, Japanese Unexamined Patent Publication JP-A 2002-314330 discloses an antenna apparatus including: a dielectric base body; plural feeder radiation elements that are formed on a surface of the base body and has feeder electrodes and radiation electrodes; and a substrate for fixing the base body, in which a common feeding point for feeding power to the feeder radiation elements, stubs are provided so as to expand continuously from the feeding point on a surface of the substrate or on surfaces of the base body and the substrate, and the feeder electrodes of the feeder radiation elements are connected to a matching point of stubs that are decided on the basis of an effective line length of the radiation electrodes. According to this disclosure, the respective feeder radiation elements are excited at resonance frequencies that depend upon an effective line length of the radiation electrodes. In this case, the feeder electrodes of the respective feeder radiation elements are connected to the matching point of the stubs, which is an optimal stub length, for each of the feeder radiation elements. Therefore, satisfactory resonance characteristics are obtained at the respective resonance frequencies in the respective feeder radiation elements, and necessary bandwidths can be secured in frequency bands to which the respective resonance frequencies belong.
However, in the conventional surface mounting type antenna 61 shown in FIG. 4, there is a problem that, in order to match an operation frequency of the surface mounting type antenna 61 to a lower frequency f1 and a higher frequency f2 of a radio signal used in a communication system, it is necessary to adjust lengths and pitches of the spiral radiation electrodes 62 and 63, and the adjustment requires many labor hours.
In addition, there is also a problem that, when it is attempted to increase a dielectric constant of the base body 66 to reduce a size of the surface mounting type antenna 61, since an unnecessary resonance mode occurs unexpectedly between the spiral long radiation electrodes 62 and 63 and the ground conductor layer 73, and stable antenna characteristics applicable to two frequencies is not obtained, it is difficult to reduce a size of the surface mounting type antenna 61.
Further, in the antenna for a mobile communication terminal disclosed in JP-A 2002-204120, there is a problem that it is difficult to apply surface mounting to a mounting substrate.
Moreover, in the antenna apparatus disclosed in JP-A-2002 314330, there is a problem that since the radiation electrodes have a plane pattern, a size of the antenna increases, and it is difficult to reduce a size of the antenna.